Necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants that afflicts 3,000 to 4,000 babies in the United States each year. Many factors contribute to the development of NEC, mainly prematurity, enteral feeding, intestinal hypoxia/ischemia, and bacterial colonization. Despite significant morbidity and mortality, the etiology and pathogenesis of NEC is poorly understood. A recent paper from our laboratory has demonstrated a dramatic endogenous overproduction of IL-18 in the ileum of neonatal rats with severe NEC-like injury. In this proposal, we want to further clarify the role of IL-18 during NEC pathogenesis. In addition to pathologic effects in the ileum, severe NEC injury is often followed by multisystem organ failure including hepatic failure. Hepatic dysfunction is frequently associated with loss of synthetic functions, hepatocellular necrosis, and release of inflammatory mediators, such as TNF-alpha. We recently demonstrated upregulation of TNF-alpha in Kupffer cells (KC), the resident hepatic macrophage, is correlated with ileal disease severity in our neonatal rat model. In addition, we have shown increased TNF-alpha in the luminal intestinal contents of animals with NEC is attenuated when KC are inhibited, and inhibition of KC is associated with decreased intestinal damage. The central hypothesis of this proposal is that overproduction of IL-18 and TNF-alpha play an essential role in the development and progression of NEC in newborn rats. We have focused on IL-18 and TNF-alpha because we believe these cytokines are the most likely to play a significant role in disease pathogenesis. We will test the central hypothesis with the following two specific aims: 1) determine if proinflammatory IL- 18 is essential for the development of NEC and 2) determine if the development of neonatal NEC is exacerbated by concomitant alterations in production and release of pro-inflammatory TNF-alpha in neonatal rat liver. The unique and highly relevant rat experimental model of NEC will be used to complete proposed research. Results from these studies should clarify if IL-18 and/or TNF-alpha are crucial for the development and progression NEC injury in the neonatal rat model. Data obtained from these studies will be used to determine the feasibility of pursuing anti-IL-18 or anti-TNF-alpha treatment in clinical trials.